The present invention relates to digital encoding of musical signals for transmission and storage. Employing a digital transmission or storage medium for musical signals is advantageous over the older known analog transmission and storage techniques due to increased noise immunity. That is, when digital transmission and storage techniques are employed the inherent noise in the transmission medium or in the memory medium causes a much smaller adverse effect on the ultimate reproduced musical signal than in the case of analog systems.
A typical proposed digital musical encoding system known in the prior art employs an analog-to-digital converter to convert an analog input signal corresponding to musical signals into a series of digital words. Each digital word typically includes 14 to 16 bits which represent the amplitude of the analog signal at a particular point in time. According to the well known Nyquist sampling theorem, the rate at which the analog signal is sampled for generation of the digital data words must be at least twice the highest frequency to be handled by the system. Thus in a typical musical system in which the highest desired frequency to be reproduced is in the range of 15 KHz to 20 KHz, the sampling rate must be at least 30 KHz to 40 KHz.
This known prior system has a marked disadvantage in that the data rates required for the communication of the musical signals and the data storage capacity necessary for storing these musical signals in digital form is much greater than the similar data communications rate and storage requirements in analog form. For example, selecting a sampling rate of 44 KHz and a 14 bit sample size, a stereo system employing two channels would require 1.23 million bits per second. Under similar conditions employing a 16 bit sample would require 1.4 million bits per second. This data rate requirement, and the corresponding storage requirements, far exceed the current capacity of analog musical systems. As a consequence, digital musical transmission and storage systems of this type have typically specified use of video storage techniques such as video disks or video cassette recorders in order to obtain the required data rate and storage capacity. As a consequence the cost and complexity of such systems greatly exceeds that of the analog systems to be replaced.